1. Field of the Invention
The present invention is in the field of cathode ray tube fixturing devices, and particularly relates to a positioning jig for positioning a face panel and a funnel in a frit sealing process wherein the panel and the funnel are heated and sealed to each other by the intermediate layer of glass frit.
2 . Description of the Prior Art
In producing a color cathode ray tube, a frit sealing step is carried out wherein the front face panel and the funnel portion of the tube are joined together while the panel and funnel portions are held by a positioning jig. FIG. 6 of the drawings shows a conventional inclined type positioning jig. In FIG. 6, reference numeral 4 designates a frame stand which is inclined along a diagonal line. A base 5 of the fixturing device is mounted on the frame stand 4. A first abutting block 6A, a second abutting block 6B and a third abutting block 6C are mounted on the base 5 in such a manner as to be opposed to adjacent sides of a face panel 1 and a funnel portion 2. Each of the abutting blocks 6A, 6B and 6C has a panel abutting bolt 7 and a funnel abutting bolt 8 which abut against peripheral sides of the panel 1 and the funnel 2, respectively. A cone holder 9 is provided at the central portion of the frame stand 4 to position a constricted portion 2a of the funnel 2, that is, a so-called E-line portion (see FIG. 7) forming a reference circle in section at three points. A neck support 10 (FIG. 6) is provided to position a neck portion 3 integrally formed with the funnel 2 at two points. A carbon member 11 is provided inside the cone holder 9 and is adapted to directly contact the constricted portion 2a of the funnel 2. A carbon member 12 is provided on the neck support 10 and is adapted to directly contact the neck portion 3. The sealing interface between the panel 1 and the funnel 2 is indicated at reference numeral 13.
FIG. 7 shows the various abutment positions against the panel 1, the funnel 2 and the neck portion 3. The panel 1 is held at three points P.sub.1, P.sub.2 and P.sub.3, while the funnel 2 is held at three points F.sub.1, F.sub.2 and F.sub.3. The E-line portion of the funnel 2 is held at three points, E.sub.1, E.sub.2 and E.sub.3, while the neck portion 3 is held at two points, N.sub.1 and N.sub.2. In carrying out the frit seal, a frit is applied to an end surface of the funnel 2 and the panel is then aligned with the funnel on the frit. The assembly of panel 1 and funnel 2 is set on a positioning jig 14. At this time, the assembly is positioned in such a manner that the axis of the cathode ray tube is inclined at a predetermined angle from the vertical. Then, the assembly is brought into abutment against the respective abutting bolts 7 and 8 of the abutting block 6A, 6B and 6C by the combined weight of the panel 1 and the funnel 2, thus positioning the same. Then, the assembly of the panel 1 and the funnel 2 as positioned above is conveyed to a heat treating furnace to carry out the sealing of the panel 1 to the funnel 2.
The above described inclined type positioning jig has several distinct disadvantages.
(1) As the panel 1 and the funnel 2 are inclined, there is irregular wear of the abutting members of the abutting blocks 6A, 6B and 6C, the cone holder 9 and the neck support 10 so as to cause seal slippage as time goes on.
(2) The wear of the abutting members and the working error of the panel 1 and the funnel 2 cause a seal slippage.
(3) After the panel 1 and the funnel 2 are set on the positioning jig, the abutment condition of the abutting members is changed by vibration during conveyance. For example, some of the abutting bolts are separated from the panel 1 and the funnel 2, causing a seal slip.
(4) As the positioning jig is inclined, it is necessary to provide for mechanical and thermal strength to resist thermal deformation of the abutting members and the base 5 as well as the conveying device and the loading or unloading device. As a result, the weight of the jig may be on the order of 50 kg, requiring a great deal of labor for maintenance.
(5) With the positioning jig inclined, automatic motion of the loading and unloading device is rendered complicated, so there is an increased cost for automation.